Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in a fuel vapor canister coupled to the fuel tank which contains adsorbent material, such as activated carbon, capable of adsorbing hydrocarbon fuel vapor.
The fuel tank may be further coupled to a vapor recovery line (vapor recirculation line). The vapor recovery line may be configured to circulate and/or hold a percentage of refueling vapors, thus limiting the rate of fuel vapor canister loading. Fuel vapors may recirculate back to the fuel tank by flowing through the recirculation line, and then through a filler neck of the fuel tank. Further, depending on the fuel dispenser, the fuel vapors within the vapor recovery line may be returned to the fuel dispenser, thus limiting the total fuel vapor stored within the fuel vapor canister for a given refueling event. Fuel vapor recirculation lines include orifices to regulate the fuel vapor flow rate through the recirculation line.
However, as the orifices age, flow through the orifices may decrease. For example, the vapor recovery line may become blocked, and as a result fuel vapors may not circulate through the vapor recovery line, causing the canister loading rate (and total load) to increase. Excess loading of the canister may cause hydrocarbon escape to the atmosphere. Further, during refueling, the pressure in the fuel tank may increase as fuel is added to the tank. In some examples, the fuel pressure may increase to a level where the fueling is terminated before the fuel tank is full.
The inventors herein have recognized the above issues, and have developed systems and methods to at least partially address them. In one example approach a method of adjusting fuel vapor flow through a recirculation line is provided. The method may comprise adjusting an amount of fuel vapors flowing through a fuel vapor recirculation line, the line coupled on a first end to a fuel tank and on an opposite second end to a fuel fill inlet, by adjusting a position of a variable orifice valve positioned within the recirculation line, via an electronic controller. Additionally or alternatively, the adjusting the position of the valve may comprise opening the valve in response to increases in hydrocarbon emissions from a carbon canister, and closing the valve in response to increases in hydrocarbon emissions from the fuel fill inlet.
As another embodiment, a method may comprise adjusting a ratio of fuel vapors flowing through a fuel vapor recirculation line relative to a fuel vapor storage line by adjusting the position of a continuously variable valve positioned in the fuel vapor recirculation line, where the adjusting may be based on hydrocarbon emission levels from a fuel vapor canister vent line, and hydrocarbon emission levels from a fuel fill inlet of a fuel tank. The ratio may be increased by adjusting the valve to a more open position in response to increases in the hydrocarbon emission levels from the vent line, and wherein the ratio may be decreased by adjusting the valve to a more closed position in response to increases in the hydrocarbon emission levels from the fuel fill inlet.
In this way, loading of a fuel vapor canister may be reduced without increasing hydrocarbon emission levels. By adjusting the variable orifice valve to the most open position in response to increases in hydrocarbon emissions from the canister, more of the fuel vapors exiting the fuel tank may be directed to the recirculation line as opposed to the canister. Thus, the size and cost of the canister may be reduced, and the fuel efficiency of a vehicle system may be increased. Further, premature fuel shut-offs during refueling of the fuel tank may be reduced by adjusting the valve to a more open position to reduce pressure increases in the fuel tank.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.